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Next Amp Build?

Discussion in 'Shock Brother's DIY Amps' started by Phrygian77, Mar 4, 2017.

  1. Mar 4, 2017 #1
    Phrygian77

    Phrygian77 Friend of Leo's Gold Supporter

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    I'm thinking about getting another PR chassis and opening up the PT cutout to accept a Tremolux/Vibroverb transformer, and then building out a single channel AB763 minus vibrato with Tung-Sol 5881s. I've already started working on a layout for the board. I'll probably use a 5U4GB to keep the voltage down. OT would either be a Bassman/Super type or Tremolux/Vibroverb/Pro sized, depending on which will fit over on the preamp side of the chassis. The baffle in my PR cabinet has an offset 12" cutout, so I'm not sure the bigger OT will fit.
     
    Last edited: Mar 4, 2017
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  2. Mar 5, 2017 #2
    CapnCrunch

    CapnCrunch Friend of Leo's

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  3. Mar 5, 2017 #3
    Phrygian77

    Phrygian77 Friend of Leo's Gold Supporter

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    I'm familiar with Hoffman's layouts. I appreciate your post, but I discovered many years ago that I hate turrets. Being accustomed to working on Fenders with eyelets, they are infuriating to me. Anyway, I'm not completely reinventing the wheel since I'm just using part of the Princeton Reverb layout and part of the AB763 layout.
     
  4. Mar 5, 2017 #4
    Wyatt

    Wyatt Tele-Afflicted

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    Hoffman also sells a 1-channel reverb AB763 eyelet board, but it uses Fenders layout instead of Hoffman's.

    Since you don't want trem, you wouldn't have to worry about losing the tube trem from Hoffman's layout.
     
    Last edited: Mar 6, 2017
  5. Mar 6, 2017 #5
    FenderLover

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    Phrygian77 likes this.
  6. Mar 6, 2017 #6
    Phrygian77

    Phrygian77 Friend of Leo's Gold Supporter

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    That board is 12", which would just fit, but that would put some of the components further away from their respective tube sockets than I would like. I guess I could cut out the vibrato section, and mount the two remaining boards separately. That would probably work, but it would look crude.

    That's a really cool build! I've thought about doing something similar with a Vibro Champ chassis, a mini AA864/AA165 Bassman head with just the normal channel.

    I thought about using one of Allen's PTs. It's almost $20 more. That's not that big of a deal, but one thing that troubles me is, what happens when your transformer gets fried and Allen is no longer around? I'd also just like to take on the challenge of modifying the chassis for the bigger transformer.
     
    Last edited: Mar 7, 2017
  7. Mar 7, 2017 #7
    FenderLover

    FenderLover Poster Extraordinaire

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    I never thought about replacements, but mod now or (maybe) mod later I guess.

    I cut up a Princeton chassis years ago to drop a Bassman transformer into. That was a hot mess. The X-mount transformer is far easier. I'm kicking around another custom build on a Champ chassis where the Hammond 273BX already fits two of the mounting holes, just drill two mounts and two more to feed the leads, done. Big iron with KT88's on a Champ? Damn right...

    Another benefit of the X-mount is that the room underneath it is still usable in a tight chassis to add standoffs, bias circuit, filters, etc. The Fender style mounts with the huge hole really kills that available room.
     
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  8. Mar 15, 2017 #8
    Phrygian77

    Phrygian77 Friend of Leo's Gold Supporter

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    Well, I keep changing my mind about what I want to do, so I started drawing this up while I was thinking an AC30-ish type build.
     

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  9. Mar 16, 2017 #9
    M Fowler

    M Fowler TDPRI Member

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  10. Mar 22, 2017 #10
    Phrygian77

    Phrygian77 Friend of Leo's Gold Supporter

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    After playing around with the AC30 inspired 6V6 circuit in LTspice, I quickly realized that the PI, with a 1.2k bias resistor and a 47k tail, isn't going to put out enough voltage to drive the 6V6s, not more than about 12 watts at least. The schematic that I found for the Top Hat Club Deluxe uses those values, so I don't know if that was just incorrect, or those amps were really limited by the PI hitting the wall. I think a 750 ohm bias and 33k tail will work. I updated the schematic to include that change plus some of the Trainwreck Rocket tweaks. I still need to test it in LTspice.
     

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